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ADVANCED TURBULENCE MODELLING OF WINGTIP VORTICES

Alistair Revell
Computational Fluid Dynamics group, Modelling and Simulation Centre, School of MACE, The University of Manchester, UK

Karthikeyan Duraisamy
University of Glasgow, 623B James Watt Bdg., Glasgow. UK.

Gianluca Iaccarino
Department of Mechanical Engineering Institute for Computational Mathematical Engineering Stanford University Bldg 500, RM 500-I, Stanford CA 94305 - USA

Abstrakt

The performance of two 'modified' eddy viscosity models (EVM) is assessed in their application to trailing vortex flows. The curvature corrected v2 − f model Duraisamy and Iaccarino (2005) was specifically derived to account for the effects of rotation and streamline curvature, and is based on mimicking the behaviour of the equilibrium solution of Reynolds stress models (RSM) under homogeneous conditions. Focus is upon the Stress-Strain Lag (Cas) model, which was derived to capture the effects of misalignment between mean strain and turbulent stress fields, particularly for unsteady mean flows (Revell et al., 2006). In this work the model is coupled with the SST model to form the SST-Cas model, which is first validated for the case of an isolated Batchelor vortex.
Secondary to the main objective of the evaluation of EVMs, is to test an advanced unstructured meshing tool, which has the potential to offer huge economies in grid meshing. Both these goals serve a greater common purpose, which is the delivery of practical and economic alternatives to industrial users, where time and cost constraints are paramount.
Both modelling schemes are shown to respond correctly to the rotational effects of vortex flows, and the decay rates are well predicted. An unstructured mesh is used to compute the wingtip flow of Chow et al. (1997), employing ~ 8 × less cells than that required for a grid independent solution on a structured mesh. While results are encouraging and considerable time economies are made, the same level of accuracy attained on the structured mesh is not reached, and further refinement and tuning is required.